The present invention is directed to polyaxial bone screws for use in bone surgery, particularly spinal surgery. Such screws have a receiver or head that can swivel about a shank of the bone screw, allowing the receiver to be positioned in any of a number of angular configurations relative to the shank.
Many spinal surgery procedures require securing various implants to bone and especially to vertebrae along the spine. For example, elongate members, such as solid rigid rods or more flexible elongate members are often utilized that extend along the spine to provide support to vertebrae that have been damaged or weakened due to injury or disease. Such elongate members must be supported by certain vertebrae and support other vertebrae.
The most common mechanism for providing vertebral support is to implant bone screws into certain bones which then in turn support the elongate member or are supported by the elongate member. Bone screws of this type may have a fixed head or receiver relative to a shank thereof. In the fixed bone screws, the head cannot be moved relative to the shank and the rod must be favorably positioned in order for it to be placed within the head. This is sometimes very difficult or impossible to do. Therefore, polyaxial bone screws are commonly preferred.
Polyaxial bone screws allow rotation of the receiver about the shank until a desired rotational position of the receiver is achieved relative to the shank. Thereafter, a rod can be inserted into the receiver and eventually the receiver is locked or fixed in a particular position relative to the shank.
A variety of polyaxial or swivel-head bone screw assemblies are available. One type of bone screw assembly includes an open head or receiver that allows for placement of a rod within the receiver. A closure top or plug is then used to capture the rod in the receiver of the screw.